Kevin Langdon was writing several books and designing an inside-out clock. Karyn Huntting Peters was organizing a global problem-solving network. Alfred Simpson juggled multiple Web-programming projects in his free time. These three people might not have had much in common—except for their unusually high IQs.
All three belong to exclusive high-IQ societies. Mensa International, whose members' test scores must land above the 98th percentile (or one in 50), may be the most popular, but it is just one option for the discerning test taker. The Triple Nine Society demands an IQ in the 99.9th percentile, whereas the Mega Society cuts off at the 99.9999th percentile (one in one million). The memberless Grail Society claims to accept one in 100 billion people—no one has applied so far.